dc7b8dc72a
Add OAuth provider linking/unlinking endpoints, merge token service (Redis-backed, 30-min TTL), and atomic account merge executor that transfers OAuth IDs, telegram_id, email, balance, subscriptions, transactions, payments, referral data, and partner status between two user accounts. Unchosen subscription is deleted from RemnaWave with disable as fallback. Includes 39 unit tests covering all merge scenarios.